1. Field of the Invention
The present invention relates to a liquid crystal display device for full color displaying, and a method for making the same, and in particular, a method for fabricating a color filter applied to the liquid crystal display device.
2. Description of the Related Art
As is known, in a liquid crystal display device, a liquid crystal layer is sandwiched between each one pair of alignment films, transparent electrodes, color filters, transparent substrates, and polarizing filters deposited in that order from the liquid crystal layer.
Since the transparent electrode and the color filters are generally deposited on the transparent substrate, the transparent substrate provided with the transparent electrode and the color filters is hereinafter referred to as a "color filter substrate".
A method for fabricating the color filter substrate in a conventional liquid crystal display device will be described as follows.
FIGS. 10A, 10B, 10C, 10D, and 10E are schematic representations of a fabricating process for the color filter substrate.
In this process, as shown in FIG. 10A, a plurality of parallel transparent electrodes 6 are formed, at a given distance, on a surface of a transparent substrate 1. The transparent electrodes 6 are composed of ITO.
Next, as shown in FIG. 10B, a plurality of horizontal stripes 100 are formed so as to cross the transparent electrodes 6. The horizontal stripes 100 are formed by the steps of (a) applying a photo resist onto an entire surface of each of the transparent electrodes 6 and drying the photo resist, (b) exposing the photo resist layer with a mask which has slits shaped exactly like the horizontal stripes 100, and (c) removing the unexposed photo resist.
After the horizontal stripes 100 are formed, as shown in FIG. 10C, any one of the color filters 3, R, G or B, is deposited on portions of the corresponding transparent electrodes which are not covered by the horizontal stripes 100, by an electro-deposition process, a dyeing process, a printing process, or the like. Then, the color filters 3 are baked and solidified at a temperature of approximately 250.degree. C.
After the color filters 3 are formed, the horizontal stripes 100 are removed by showering an alkali solution containing, for example, sodium hydroxide while brushing them. Thus, as shown in FIG. 10D, a color filter substrate is obtained, which is not yet provided with a shading film (hereinafter called a "black mask").
Finally, a black resist is applied onto an entire surface of the color filers 3 followed by drying. Then, by exposing from the back face of the transparent substrate 1, the unexposed black resist is removed. As shown in FIG. 10E, a black mask 101 is formed on the spaces between the color filters 3.
In accordance with the process described above, a transparent substrate provided with transparent electrodes and color filters, namely a color filter substrate, is fabricated. After this, a liquid crystal display device will be completed by enclosing a liquid crystal layer between each one pair of alignment films, the color filter substrates, and polarizing filters.
In the above-mentioned conventional liquid crystal display device, since ITO forming the transparent electrodes has a low conductivity, it is difficult to have a large potential difference between one pair of electrodes opposing each other with the liquid crystal layer therebetween, and therefore the display quality is low.
Also, in the above-mentioned conventional liquid crystal display device, the shading property of the black mask depends on a quantity of carbon black in the black resist forming the black mask. Accordingly, in order to increase the shading property of the black mask, a large quantity of carbon black may be included; however, because carbon black has a relatively high conductivity, if a large quantity of carbon black is added, the black mask becomes conductive, causing a short circuit between the transparent electrodes adjoining the black mask. Thus, a large quantity of carbon black cannot be added. Accordingly, the conventional liquid crystal display device has a black mask with a low shading property and has a low quality of display.